1. Field of the Invention
The present invention relates to an organic light emitting display device. More particularly, the present invention relates to an organic light emitting display device that blocks light from being irradiated onto an oxide thin film transistor (TFT) by using a light shield formed of a source/drain metal, and a method of manufacturing the same which can reduce the number of masks to increase manufacturing efficiency.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices, which are widely used, need a backlight as a light source, and have technical limitations in brightness, contrast, and a viewing angle. Organic light emitting devices, on the other hand, self-emit light. The organic light emitting devices do not need a separate light source and have relatively better brightness, contrast, and viewing angle. Thus, interest in the organic light emitting devices is increasing.
Organic light emitting display devices emit light from an organic light emitting diode (OLED) formed in each of a plurality of pixels, thereby displaying an image. The OLED has a structure in which an emission layer is formed between a cathode for injecting an electron and an anode for injecting a positive hole. When an electron generated from the cathode and a positive hole generated from the anode are injected into the emission layer, the electron and the positive hole are combined to generate an exciton, and the generated exciton is shifted from an excited state to a ground state to emit light, thereby displaying an image.
The organic light emitting display devices are categorized into passive matrix organic light emitting display devices and active matrix organic light emitting display devices depending on a driving mode.
The passive matrix organic light emitting display devices have a structure in which a plurality of pixels are arranged in a matrix type without including a thin film transistor (TFT). For this reason, the passive matrix organic light emitting display devices have high power consumption, and are limited in resolution.
On the other hand, active matrix organic light emitting display devices have a structure in which a plurality of pixels each include a TFT and are arranged in a matrix type. Each of the plurality of pixels is driven according to the turn-on of the TFT and a voltage charged into a storage capacitor.
Therefore, the active matrix organic light emitting display devices have lower power consumption and a higher resolution than the passive matrix organic light emitting display devices. An active matrix OLED is suitable for display devices that require a high resolution and a large area. For reference, in the present specification, an active matrix organic light emitting device is briefly referred to as an organic light emitting device.
FIG. 1 is a cross-sectional view illustrating a structure of a TFT formed in a pixel of a related art organic light emitting display device.
Referring to FIG. 1, a lower gate 10 is formed on a substrate, and a gate insulating layer 20 is formed to cover the lower gate 10.
An active layer 30 is formed at a portion of a top of the gate insulating layer 20 which overlaps the lower gate 10, and an etch stop layer 40 is formed at the active layer 30.
A portion of the etch stop layer 40 is etched to expose the active layer 30, and a source 52 and a drain 54 are formed to contact the exposed active layer 30.
A protective layer 60 is formed to cover the gate insulating layer 20, the etch stop layer 40, the source 52, and the drain 54. An upper gate 70 is formed at a portion of a top of the protective layer 60 which overlaps the active layer 30.
A TFT is formed in an etch stop (ES)-double gate (DG) structure which includes the lower gate 10, the gate insulating layer 20, the active layer 30, the source 52, the drain 54, the protective layer 60, and the upper gate 70.
In the TFT of the related art, a turn-on/off capacitance is large, and short circuit occurs between a source/drain metal and a metal of an upper gate. For this reason, there is a high possibility that a hot spot and a dark spot occur.
Moreover, a kickback increases, and the boosting efficiency is reduced, causing a problem of an image quality of an OLED panel. The TFT and a storage capacitor are separately formed, and an area occupied by the TFT and storage capacitor increases, causing a reduction in an opening of a pixel. For this reason, it is difficult to apply a high-resolution OLED panel.
To overcome such limitations, the TFT should be formed in a coplanar structure. However, since an oxide TFT has vulnerable characteristic in which a characteristic of a device is changed by light, a light shield should be separately formed under the active layer 30.
Moreover, a total of eight masks are used in a process of manufacturing a TFT. As such, the process time and cost increase.